1. Field of the Invention
The present invention relates to a communication network control system, a control method, a node and a program, and more particularly, to a communication network control system, a control method, a node and a program in a hierarchical communication network formed of a plurality of links having different attributes.
2. Description of the Related Art
Among communication network control systems enabling path setting from a transmission source node to a destination node in a conventional communication network formed of a plurality of links having different attributes are, for example, ITU-T Recommendation G. 805 and the technique disclosed in Japanese Patent Laying-Open (Kokai) No. Heisei 11-177562.
In ITU-T Recommendation G.805, used as a method of regulating a complicated communication network constituted by a plurality of links having different attributes is taking the sub-network concept to use a layer structure relationship in the network.
A communication network shown in FIG. 12, for example, has such a layer network structure as shown in FIG. 13. Here, a domain-A, a domain-B, a domain-C, a domain-D and a domain-F are sub-networks formed of nodes which conduct switching on a granularity of an STS-1 (Synchronous Transport Signal-1). On the other hand, a domain-G is a sub-network formed of nodes which conduct switching on a granularity of OC-48 (Optical Carrier-48). The domain-A, the domain-B, the domain-C, the domain-D and the domain-F are all connected through the domain-G.
The communication network shown in FIG. 12 is accordingly a layer network formed of an STS-1 layer including the domain-A, the domain-B, the domain-C, the domain-D and the domain-F and an OC-48 layer including the domain-G.
One example of cross-connects which conduct switching on the granularity of the STS-1 is a SONET (Synchronous Optical Network) cross-connect. FIG. 14 is a conceptual diagram showing a SONET cross-connect. As shown in the figure, the SONET cross-connect enables a signal applied through an input port to be switchedly output to a different output port on a time slot basis. At this time, it is possible to assign a label to a time slot to manage correspondence between an input label and an output label, thereby handling data transmitted in time slots as LSP (LABEL Switched Path). The figure shows how data of a time slot #1 of a signal applied to a port 1 is output with its time slot switched to a time slot #3 as a signal output through a port 4.
One example of cross-connects which conduct switching on the granularity of the OC-48 is a wavelength cross-connect. FIG. 15 is a conceptual diagram of a wavelength cross-connect. As shown in the figure, the wavelength cross-connect is to output an input signal switchedly on a wavelength basis as an output signal while maintaining the order of its time slots. At this time, data transmitted in wavelength can be handled as LSP by assigning a label to a wavelength (port) and managing correspondence between an input label and an output label. The figure shows how data of the wavelength of the port 1 is output with its wavelength switched to the wavelength of the port 4.
FIG. 16 is a structural diagram of the communication network control system recited in Japanese Patent Laying-Open (Kokai) No. Heisei 11-177562. As shown in the figure, the communication network control system is formed of an operating system 801, a layer network information collecting function 802, a layer network forming function 803, a connectable point searching function 804, a virtual link generating function 805 and a path setting function 806.
Then, upon collecting network information (kind of transmission rate, distinction between synchronous and asynchronous networks, etc.) in the same layer from the operating system 801 of a network domain, the layer network information collecting function 802 sends out a layer network formation request to the layer network forming function 803. Upon receiving the formation request, the layer network forming function 803 forms the layer network in question based on the network information and when a lower-order layer network exists, forms the network based on connectability information collected from the lower-order layer network.
Connectability information from the lower-order layer may be directly collected by the layer network information collecting function 802 and applied to the layer network forming function 803 together with the network information or may be collected by the layer network forming function 803 through the layer network information collecting function 802. Next, the virtual link generating function 805 generates a virtual link as information about connectability between access points of the formed layer network based on the connectability information collected from the lower-order layer network.
More specifically, a lower-order layer network exists for a layer network having the function of generating a virtual link and also in the lower-order layer network, the layer network forming function 803 similarly forms a layer network, and the connectable point searching function 804 searches for connectability between access points of the formed layer network, generates connectability information and notifies the higher-order layer network of the information.
At the time of thus managing the communication network as divisional networks of layer structures formed based on network information collected from the operating system 801 of each network domain, according to the invention recited in Japanese Patent Laying-Open (Kokai) No. Heisei 11-177562, a virtual object link is set as connectability information in each layer network (more precisely, layer networks excluding the lowest-order layer network).
FIG. 17 shows an example of a layer network structure in a case where the communication network control system recited in Japanese Patent Laying-Open (Kokai) No. Heisei 11-177562 is applied to the communication network shown in FIG. 12. With reference to FIG. 17, the layer network is formed of an STS-1 layer and an OC-48 layer. The STS-1 layer has five sub-networks, a domain-A, a domain-B, a domain-C, a domain-D and a domain-F. The domain-A, the domain-B, the domain-C, the domain-D and the domain-F have clients (X, Y, Z, U, V, W), respectively, and between their relay nodes (a, b, c, d, e, f), virtual links indicated as wide white lines are set.
The OC-48 layer has a sub-network, a domain-G. The domain-G includes nodes (A, B, C, D, E, F).
In GMPLS (Generalized Multiprotocol Label Switching) discussed in IETF (Internet Engineering Task Force), the concept of Forwarding Adjacency (FA) is introduced into a virtual link generated between a transmission source node and a destination node of a path which is cut through a higher-order layer switch (IP (Internet Protocol) router, ATM (Asynchronous Transfer Mode) switch or the like) and switched by a lower-order layer switch (optical cross-connect, SONET cross-connect or the like). FA enables accommodation of a plurality of higher-order layer paths.
In the layered communication network control system conformed to ITU-T Recommendation G.805, as shown in FIG. 13, however, formation of a path between two sub-networks in the STS-1 layer is enabled only when a path of the lower-order OC-48 layer network is set up end-to-end. When the higher-order layer network (STS-1) knows that a path of the lower-order layer network (OC-48) is set up, it is therefore allowed to know that relay nodes of a higher-order layer sub-network which are end points of the lower-order layer path can be connected. On the other hand, when the high-order layer network fails to know that a path of the lower-order layer network (OC-48) is set up, whether relay nodes of a higher-order sub-network are connectable or not is unclear.
Under these circumstances, in ITU-T Recommendation G.805, for example, in a case of FIG. 18, with paths set between the node A and the node C and between the node C and the node E in the OC-48 layer, when a new path needs to be set up end-to-end from the domain A to the domain D in the STS-1 layer, since the domain A knows that the virtual link of the STS-1 layer exists between the node a and the node c (via the node b) and between the node c and the node e (via the node d), set up the path of the STS-1 end-to-end between the domain A and the domain D through the virtual link. However, since it is impossible to set up a path of the OC-48 directly connecting the node a and the node e and with the path as a virtual link, to set up a path of the STS-1 end-to-end between the domain A and the domain D, the route of the STS-1 path could not be the shortest, which disables effective use of resources.
On the other hand, the art disclosed in Japanese Patent Laying-Open (Kokai) No. Heisei 11-177562 solves the above-described problem and, when with a path set between the node A and the node F in the OC-48 layer as shown in FIG. 19, an end-to-end path needs to be newly set from the domain A to the domain D in the STS-1 layer, setting a new path of the OC-48 between the node F and the node E assuming that a free path exists between the node A and the node F leads to setting of an end-to-end path of the STS-1 from the domain A to the domain D.
However, in the STS-1 layer it is only known that no virtual link exists between the domain A and the domain D and it is not known that setting a virtual link between the domain F and the domain D enables setting of an STS-1 path between the domain A and the domain D via the node f, resulting in making a request for setting an OC-48 path between the domain A (node a) and the domain D (node e) from the OC-48 layer. As a result, OC-48 paths will be overlapped between the node a and the node f to cause a new problem that resources can not be effectively used.